The present invention relates to a transfer sheet suitable for forming high-precision patterns for layers such as electrode layers, dielectric layers and barrier layers in plasma display panels (hereinafter PDPs for short), field emission displays (FEDs), liquid crystal display devices (LCDs), vacuum fluorescent displays, hybrid integrated circuits, etc., and a pattern-forming method.
As well known so far in the art, such patterns are formed by the pattern-wise coating of an ink for conductors or insulators on a suitable substrate of such as a glass or ceramic substrate by means of screen printing, and the firing of the substrate, thereby obtaining a thick pattern in close contact with the substrate. According to this technique, for instance, fine lines having a line width of 100 .mu.m and a height of 100 .mu.m are formed by repeating superposition printing plural times.
However, the method of forming a pattern by repeating screen pattern printing many times have several problems. First, the expansion and contraction of the screen used for printing occurs unavoidably. In most applications where various patterns are formed while they are superposed one upon another, they are susceptible to misalignment. Second, the screen used as a printing plate tends to give rise to pattern distortions, so making it difficult to form micro patterns. Third, wiping is necessary for each printing because of the migration of the pattern-forming material to the back side of the screen plate; that is, automation is difficult. Fourth, pattern size achievable by screen printing is at most about 100 .mu.m for width, and pattern shape is about 0.5 as expressed by a half width-to-bottom width ratio, where the half width is a width of a pattern-forming layer at a position half the height of the pattern-forming layer. For a barrier layer in a PDP which should be coated at an as-dried thickness of about 150 .mu.m to about 200 .mu.m, for instance, it is required to increase its bottom area, and so it is impossible to form any fine pattern. For a multilayer pattern, layers are stacked one upon another while alignment is carried out per layer because it cannot be formed in one operation. However, this offers a problem that it is difficult to improve alignment precision. Further, it is impossible to form a thick pattern having a high aspect ratio because the ink tails due to its fluidity. Furthermore, difficulty is involved in condition controls for the purpose of preventing contamination with foreign matters or the like because operations must be carried out in an open system, and so much time is needed for pattern fabrication.
There is also known a so-called sand blasting technique wherein a pattern-forming layer is solid coated on a substrate by repeating screen printing many times, then using a photosensitive resist to form a sand blasting mask on the pattern-forming layer, and finally jetting an abrasive for the patterning of the pattern-forming layer.
However, a pattern-forming method making use of this sand blasting technique, too, has a problem that a superposition printing step is not only time-consuming but also condition controls are difficult to perform because operations must be carried out in an open system. Further, coating and drying must be repeated for each layer to be formed, followed by patterning. This leads to another problem that much installation cost is not only needed but also much space is need for such installations.
A first object of the present invention is to provide a transfer sheet suitable for forming micro patterns for electrodes, resistors, barriers, etc. in image display devices such as PDPs and liquid crystal displays, thermal heads, integrated circuits and the like.
A second object of the present invention is to provide a pattern-forming method of forming a pattern having improved surface smoothness, a uniform thickness and high profile precision for a reduced time of period in high yields.